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Regional Water Recycling Plant No. 1 (RP-1)
Regional Water Recycling Plant No. 1 (RP-1) is located in the City of Ontario near the intersection of State Highway 60 and Archibald Avenue. This facility was originally commissioned in1948 and has undergone several expansions to increase the design wastewater treatment capacity to the current 44.0 million gallons per day (mgd) and biosolids treatment capacity equivalent to a wastewater flow rate of 60.0 mgd. This facility serves the Cities of Ontario, Rancho Cucamonga, Upland, Montclair, Fontana and an unincorporated area of San Bernardino County.
2450 E. Philadelphia Avenue
Ontario, California 91761
Fax (909) 947-2598
RP-1 includes several treatment processes that contribute to providing a quality recycle water pursuant to the State of California Title 22 regulations. The major treatment processes include preliminary and primary treatment, primary effluent flow equalization and diversion, secondary treatment, tertiary treatment and biosolids treatment as illustrated in figure 1. In addition, each treatment process is integrated with instrumentation and control systems for controlling and monitoring various aspects of their operations. This overall facility instrumentation and control system is called the Supervisory Control and Data Acquisition (SCADA) System. The following subsections, briefly describe the functionality of each treatment area provided at RP-1.
Preliminary and Primary Treatment
Preliminary and primary treatment are physical processes. Preliminary treatment consists of measuring (metering) the quantity of wastewater that flows into the facility, removing large objects and materials with mechanically operated course screens and removing sand and gritty material (inorganic materials that will not decompose). These materials are stored in large bins and subsequently disposed of at a landfill.
Following preliminary treatment, the wastewater is distributed equally to primary treatment settling tanks that allow the wastewater flow to slow down enough to settle out the heavy solids (organic materials that will decompose) by gravity. To enhance settling of these solids, chemicals including ferric chloride and a poly electrolyte (Polymer) are added to the wastewater. These chemicals help to clump the solids into heavier particles that settle more readily. Typically, primary treatment removes about 65% of the organic solids contained in the wastewater and these solids are referred to as biosolids.
The settled biosolids are continuously removed from the primary settling tanks and transferred to a process where it is concentrated (or thickened) and subsequently pumped to the biosolids handling facilities located at RP-1.
Primary Effluent Flow Equalization and Diversion
After removing the heavy organic solids, the primary treated wastewater (primary effluent) enters a pumping facility and is pumped to secondary treatment. When the amount of primary effluent exceeds the RP-1 secondary treatment capacity, some of the primary effluent can be routed and temporarily stored in basins to help equalize the flow to secondary treatment. During the off-peak flow periods, the stored primary effluent is returned to the pumping facility and pumped to secondary treatment. In addition, primary effluent can be diverted to the RP-5 facility for further treatment and to meet recycled water demands as needs may dictate.
Secondary treatment at RP-1 is a biological process containing millions of microorganisms that can only survive and multiply in an environment containing free oxygen that is dissolved in the water and a food source. This method for treating wastewater is referred to as the activated sludge process. The suspended and dissolved solids in the primary effluent serve as the food source and oxygen is provided by pumping and diffusing air (similar to how air is pumped and diffused in a fish aquarium) into large tanks containing the microorganisms and primary effluent. The mixture of microorganisms, primary effluent and dissolved oxygen is referred to as Mixed Liquor Suspended Solids (MLSS). After the aeration period, the MLSS is transferred to tanks where it is allowed to settle by gravity leaving a clear liquid referred to as secondary effluent.The secondary effluent is then transferred to tertiary treatment while the settled MLSS is returned to the aeration tanks to maintain the appropriate population and cultures of microorganisms. Return of the MLSS from the secondary clarifier tanks to the front of the aeration tanks is referred to as return activated sludge (RAS). Return of the MLSS from the discharge end of the aeration tanks to the front of the aeration tanks is referred to as ML-RAS. As the microorganisms multiply, the amount of food available in the primary effluent will become insufficient and the quality of treatment can degrade. Therefore, a portion of the MLSS or RAS is wasted from the activated sludge process in order to maintain a balance between the food source and microorganisms that will produce the highest quality of treatment. This wasting is referred to as waste activated sludge (WAS). The WAS is transferred to a process where it is concentrated and subsequently transferred to the biosolids handling facilities at RP-1.
Although the activated sludge treatment process produces a high quality of treated wastewater, the State of California, under Title 22 regulation requires the ammonia level in the treated wastewater not exceed a certain limit. Excessive ammonia in the wastewater can have detrimental toxic effects on the environment particularly for aquatic life. Therefore, the biological secondary treatment process at RP-1 is designed to remove nutrients such as ammonia, nitrate and phosphate from the wastewater. This is typically
referred to as Bio-Nutrient Removal (BNR).
BNR is accomplished by modifying the activated sludge process so that nitrification and de-nitrification will occur in specific zones within the aeration tanks. These zones are referred to as Oxic (meaning free dissolved oxygen) and Anoxic (meaning devoid of free dissolved oxygen). Nitrification naturally occurs in our rivers, streams and lakes. It is a process whereby microorganisms combined with bio-degradable organic matter, dissolved oxygen in the water and time converts Ammonia-nitrogen to Nitrite-nitrogen to Nitrate-nitrogen which is a more stable organic compound, but can still be detrimental to the environment. Therefore, the activated sludge process is also designed to achieve de-nitrification. De-nitrification is a process similar to the nitrification process only dissolved oxygen in the water is depleted. In the absence of
dissolved oxygen, the microorganisms will utilize the oxygen molecules from the nitrogen compounds for their respiration leaving only the nitrogen that is released to the atmosphere as an inert nitrogen gas.
Secondary treatment generally removes the remaining primary effluent suspended and dissolved solids in addition to reducing the level of ammonia, nitrate and phosphate. The solids remaining after secondary treatment typically consists of very fine suspended particles that are readily removed by filtration. Therefore, the nitrified and de-nitrified secondary effluent flows by gravity to tertiary treatment containing a network of filters designed to remove in excess of 99% of the remaining total solids. The secondary effluent flow is equally distribute to a number of filters containing sand and anthracite coal media that are similar to filters used for swimming pools only on a much larger scale.
As the filters become clogged, they are backwashed one at a time and returned to service. A typical filter run can take 24 to 48 hours before it requires backwashing. The waste backwash water is transferred to settling tanks where the solids captured through filtration are allowed to settle by gravity and are subsequently pumped back to primary treatment co-mixed with the solids removed from the primary settling tanks and transferred to the RP-1 Solids Handling facilities. To enhance the backwash solids settling, a coagulating chemical (aluminum sulfate or alum) is added to provide an ion charge to clump the solids into heavier particles that settle more readily.
Reclaimed Wastewater Disinfections
Before the filtered reclaimed wastewater (tertiary effluent and therefore, recycled water) can be used for irrigation and groundwater recharge purposes and or discharged to any other body of surface water, it must be disinfected to comply with the State of California Title 22 bacteriological water quality regulations. This water quality requirement is equal to the bacteriological water quality requirement for potable drinking water as stipulated in the Federal Safe Drinking Water Act regulations.
Disinfection can be somewhat complicated because of the physical, chemical and biological aspects of the recycled water. The disinfecting agent must be well mixed and remain in contact with the recycled water for a minimum time period referred to as Contact Time (CT) to ensure no pathogenic organisms (i.e. disease bearing bacteria and viruses) remain in the water. The unit of measure used to express the CT is milligram-minutes per liter (mg-min/l). The minimum CT requirement is 450 mg-min/l.
The disinfection process is accomplished in chlorine contact tanks where sodium hypochloride, as a liquid chlorine bleach is added to and instantaneously mixed with the recycled water as it enters the tanks. The chlorine contact tanks include baffles to further enhance mixing and contact of the bleach and recycled water. The CT is calculated based on the amount of recycled water being disinfected and samples are taken to measure the bacteriological water quality. The bacterial water quality is measured and express as a Most Probable Number per 100 Milliliters (MPN/100 ml) of sample. The maximum limit is less than 2.2 MPN/100 ml.
Upon being disinfected, the recycled water flows by gravity from the chlorine contact tanks to the recycled water pumping stations at RP-1. From those pumping facilities, the water is pumped into the recycled water distribution and storage system and utilized for beneficial reuse and ground water recharge.
When the demand for recycled water is less the amount of water being produced, the excess recycled water is discharged to the Cucamonga Creek. This creek is tributary to the Santa Ana River. However, before the recycled water is discharged to Cucamonga
Creek, it must be dechlorinated as required by the State of California Title 22 regulations. The purpose for dechlorination is to ensure there is no detrimental impact by the chlorine on the environment and aquatic life. This means the amount of chlorine bleach remaining in the recycled water must be neutralized.
Dechlorination is accomplished by adding sodium bisulfite, a liquid chemical that neutralizes the chlorine bleach residual remaining in the recycled water. The sodium sisulfite is mixed with the recycled water in a similar fashion as the chlorine bleach and only requires a few minutes to neutralize the remaining chlorine.
Both the disinfection (chlorination) and dechlorination processes are automatically controlled to maintain specific residuals. SCADA system instrumentation is provided to measure the recycled water chlorine bleach residual, control the amount of chlorine bleach being pumped for a preset chorine residual setpoint and to monitor and
adjust those activities. The same level and sophistication of control and monitoring instrumentation is provided for the sodium bisulfite application for maintaining a zero chlorine bleach residual in the recycled water before it enters the Cucamonga Creek.
The biosolids handling facilities at RP-1 consist of three process components including biosolids thickening, treatment and dewatering.
The biosolids removed from primary treatment (including the tertiary treatment filter backwash biosolids) and secondary treatment WAS contain a significant amount of water. To further separate the water from the biosolids, two process forms to thicken (or concentrate) the biosolids are provided at RP-1. They include Gravity Thickening (GT) for the primary treatment biosolids and Dissolved Air Floatation (DAF) thickening for the secondary treatment WAS biosolids.
Gravity Thickening (GT): The GT process operates similarly to the primary treatment settling tanks; only the biosolids are held in the tanks for a longer period of time to concentrate by gravity at the bottom of settling tanks and are subsequently pumped out. Primary treatment biosolids concentrations typically range from about 1 to 3 percent total solids. This means the dry weight or density of a given volume of biosolids mixed with water would be 1 to 3 percent of the total volume. Gravity biosolids thickening can increase the density to about 4 to 5 percent. This makes a significant difference in the amount of water contained in biosolids removed from the GT units.
Dissolved Air Floatation Thickening:The DAF process is provided to concentrate the secondary treatment WAS biosolids. Typical WAS biosolids concentrations are about 0.5 percent total solids. DAF thickening can typically increase the density of the biosolids to 4 to 6 percent. This is accomplished by air pressurizing of water so the oxygen dissolves in the water. This pressurized water is mixed with the WAS biosolids as it enters the DAF unit and the pressure is released at the same time. As the pressure is released, the dissolved oxygen comes out of solution in the form of tiny air bubbles.
The WAS biosolids particles collect unto to the air bubbles and float to the surface of the tanks (this action is similar to what happens when you shake a carbonated soft drink and remove your thumb from the container opening). As a result, a thick concentrated layer of biosolids is formed on the surface of the tank and skimmed into a hopper for subsequent removal by pumping. To enhance the biosolids collection unto the air bubbles and to improve thickening, a coagulant chemical (Polyelectrolyte or Polymer) is used to clump the biosolids particles into larger particles.
The thickened biosolids from the GT and DAF units are co-mixed and pumped to the biosolids treatment units. These units are referred to as anaerobic digesters which are treatment units that reduces the volume of organic matter by decomposition of the biosolids into relatively stable organic and inorganic compounds from which water will separate more readily. In several ways, anaerobic digestion functions similarly to the human stomach when it digests food. Unlike the activated sludge process, the anaerobic
digestion process is carried out in the absence of free oxygen by anaerobic microorganisms. Wastewater biosolids are typically about 70 percent organic and about 30 percent inorganic or mineral. Much of the water in the biosolids is what is called “bound” water which will not readily separate from the biosolids. The anaerobic microorganisms’ breakdown the complex molecular structure of the biosolids which results in releasing the “bound” water. During this release process, the microorganisms obtain oxygen from the water molecule and food from the remaining organic matter.
Time and temperature greatly affects how rapid anaerobic decomposition of the biosolids will occur and the quantity and quality of byproducts such as carbon dioxide, hydrogen sulfide and methane gases produced as a result of the decomposition.
At RP-1,anaerobic digestion occurs in three phases including acid, thermophilic and mesophilic phases. This allows control on the time and temperature for digestion and stabilization of the biosolids and production of usable methane gas to fuel engine generators that produce electrical power.
Acid Phase Digestion - In this phase of digestion, the microorganisms attack the biosolids soluble and dissolved organic matter such as sugars. From these reactions, organic acids and gases such as carbon dioxide, hydrogen sulfide and low levels of methane are formed. This is known as the acid fermentation phase of anaerobic digestion and this process proceeds rapidly. The operating temperature for this phase is maintained at 100 degrees F.
Thermophilic Phase Digestion - When completed, the biosolids are transferred from the acid phase digester to thermophilic anaerobic digester units. The thermophilic digesters are operated and maintained at 127 degrees F. This higher temperature provides an environment conducive to a culture of anaerobic microorganisms that will decompose the biosolids organic matter at a higher rate. Therefore, more biosolids can be processed over a shorter period of time. Some acid phase digestion stills occurs in this phase resulting in further release of water from the biosolids. More importantly, this phase rapidly intensifies the decomposition, stabilization and gasification of the biosolids organic matter such as proteins and amino acids resulting in the production and predominance of relatively high quality methane gas. The methane gas is odorless and highly flammable and is used as a fuel source for operating engine generators to produce electrical power.
Mesophilic Phase Digestion - Upon the biosolids being processed through the thermophilic digestion phase, it is transferred to the mesophilic digester units that are operated at a maintained temperature of 98 degrees F. Digestion of the biosolids organic matter continues in this phase of the digestion process only at a slower rate with additional production of methane gas. At this point, the biosolids are relatively stable and most of the “bound” water has been released to enhance the dewaterability of the biosolids.
The relatively stable biosolids are removed from the mesophilic phase digester units on a rotating basis and transferred to the biosolids dewatering facilities. Currently, this facility includes mechanical equipment referred to Belt Filter Presses (BFPs) that are designed to remove water from the biosolids. The biosolids dewatering operation consists of three steps including conditioning, gravity drainage and compression.
Biosolids Conditioning: The biosolids conditioning step is very important and involves the addition of polymers that will help to agglomerate the biosolids particles into flocs and thus provide the initial separation of the solids from the water. This step also conditions the biosolids to build a structure into the solids flocs so they can withstand gradually increasing pressure and shearing action.
Biosolids Gravity Drainage: After conditioning, the flocculated biosolids are deposited onto the gravity drainage section of the BFP. Gravity drainage occurs on a moving belt where the free water created during the conditioning step drains by gravity through minute pores in the belt. This leaves behind a partially dewatered sheet of biosolids. The importance of proper conditioning can be observed at this point. Without proper conditioning, the biosolids will simply pond in the gravity drainage section and run out to the edges of the belt.
Biosolids Compression: As the biosolids travel through the gravity drainage section of the BFP, it enters the compression section of the BFP. This section consist of two tensioned porous belts and a series of rollers that sandwich the biosolids to remove additional water. In traveling around the rollers, shear and compression forces are induced to squeeze out water from the biosolids.
The dewatered biosolids characteristic after the compression step is similar to moist mud and is referred to as “Cake”. The cake can typically range from about 16 to 20 percent solids. This means if you had one ton (2000
pounds) of 18 percent biosolids and removed 100 percent of the remaining water, the dry weight of the biosolids would be 360 pounds. Therefore, the higher the cake percent solids, the less water it contains and more solids can be disposed of in the same volume of biosolids.
After the biosolids compression step, it is scraped off the BFP belt and deposited onto a conveyor system. From the conveyor system, it can be stored in hoppers or deposited into trucks and subsequently hauled to the IERCF to be made into compost.
Recycling Plant No. 1
2450 E. Philadelphia Ave.
Ontario, California 91761
Fax (909) 947-2598